Since the night of 2026-07-16 production keyed the rate limiter on
Cloudflare edge IPs instead of visitor IPs: every visitor routed through
the same edge shared one 175-req/15min bucket, causing widespread 429s
(confirmed by probing: sequential requests alternated 200/429 across
fresh and exhausted buckets).
Root cause: 'trust proxy' used a fixed hop count (TRUST_PROXY=1), which
silently breaks whenever the proxy chain gains or loses an
X-Forwarded-For entry (e.g. a Cloudflare-side change).
- TRUST_PROXY now accepts a comma-separated subnet list; the new default
'loopback,uniquelocal,cloudflare' expands Cloudflare's published IP
ranges so Express skips trusted proxies no matter how many entries
they add. Plain numbers keep the legacy hop-count behavior.
- If resolution still stops at a Cloudflare address (visitor missing
from X-Forwarded-For entirely), the limiter key falls back to
cf-connecting-ip — safe because request.ip can only be a Cloudflare
address when the whole chain to it is trusted.
- CIDR matching uses Node's built-in net.BlockList (no new dependency).
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Thomas Durieux